Conventional portable telephones have incorporated therein a sound generator (ringer) for notifying the user of incoming calls with sound, i.e., with a vibration having a frequency in the audible range and a vibration generator for notifying the user of incoming calls with a vibration perceivable by the human body and having a frequency, for example, of up to hundreds of hertz. One of the two generators is selectively usable according to the situation.
However, small devices such as portable telephones have little or no excessive space for accommodating both the sound generator and the vibration generator, and therefore encounter the problem of becoming greater in size if equipped with the two generators.
Accordingly, the present applicant has proposed a portable telephone as shown in FIG. 9 (JP-A No. 14194/1998). The proposed portable telephone comprises a flat case 11 having an antenna 1 and provided on the surface thereof with a speech receiving portion 12 for outputting the voice of incoming speech, manual buttons 14 such as numerical keys, a speech delivery portion 13 for inputting the voice of outgoing speech, etc. Provided in a suitable portion of the interior of the case 11 is a notifying unit 2 for notifying the user of incoming calls with sound, vibration or both sound and vibration.
The notifying unit 2 comprises a first vibrator drivable with a first drive signal at a frequency in the audible range for producing sound waves, a second vibrator drivable with a second drive signal at a second frequency (up to hundreds of hertz) lower than the first frequency for producing a vibration, and a signal generator circuit for producing the first drive signal and the second drive signal. The first vibrator and the second vibrator are housed in a common casing. The first vibrator comprises a coil attached by a first diaphragm to the casing, while the second vibrator comprises a magnet attached by a second diaphragm to the casing. The magnet is formed with a magnetic gap having the coil of the first vibrator accommodated therein.
Stated more specifically with reference to FIG. 2, the notifying unit comprises as housed in a cylindrical casing 21 a first vibrator 4 for producing sound waves mainly and a second vibrator 3 for producing vibration mainly. The casing 21 has a compact structure in its entirety and comprises a hollow cylindrical body 22, an annular front cover member 24 having a sound emitting aperture 25 and attached to an open front side of the body 22, and an annular rear cover member 23 attached to an open rear side of the body 22.
The first vibrator 4 comprises a circular first diaphragm 41 having its peripheral portion held between the casing body 22 and the front cover member 24, and a coil 42 fixed to the rear side of the first diaphragm 41. The first vibrator 4 has a resonance frequency in an audible range in excess of hundreds of hertz.
On the other hand, the second vibrator 3 comprises an annular second diaphragm 34 having its peripheral portion held between the casing body 22 and the rear cover member 23, an outer yoke 32 secured to the inner peripheral portion of the second diaphragm 34, a permanent magnet 31 magnetized axially thereof (vertical direction) and fixed to the front side of the outer yoke 32, and an inner yoke 33 fixed to the front side of the magnet 31. The coil 42 of the first vibrator 4 is accommodated upwardly or downwardly movably in an annular magnetic gap defined by opposed faces of the outer yoke 32 and the inner yoke 33. The second vibrator 3 has a low resonance frequency of lower than hundreds of hertz.
FIG. 11 shows the vibration characteristics Cs of the first vibrator 4 and the vibration characteristics Cv of the second vibrator 3. The vibrators 4, 3 exhibit a peak in amplitude at the resonance frequencies Fs, Fv, respectively.
Accordingly, great notification effects are available by feeding a sound drive signal and a vibration drive signal of these respective resonance frequencies Fs, Fv to the coil 42 of the notifying unit 2.
More specifically, a sound drive signal Ds of a frequency (for example, about 2 kHz) in match with the resonance frequency Fs as shown in FIG. 10, (a) is fed to the coil 42 when notifying with sound, and a vibration drive signal Dv′ of a frequency (for example, about 100 Hz) in match with the resonance frequency Fv as shown in FIG. 10, (b) is fed to the coil 42 when notifying with vibration.
When the sound drive signal Ds is fed to the coil 42 of the notifying unit 2, the coil 42 produces an axial drive force by virtue of the relationship between the magnetic lines of force extending through the magnetic gap radially thereof and the circumferential current flowing through the coil 42 according to the Fleming's left-hand rule. Since the drive force acts at the frequency of the resonance point, the first vibrator 4 resonates to generate sound waves, while the second vibrator 3 remains almost free of vibration because the resonance point thereof is different. The generation of sound waves gives audio notification of an incoming call.
On the other hand, when the vibration drive signal Dv′ is fed to the coil 42 of the notifying unit 2, the coil 42 similarly produces an axial drive force. Since the resonance point of the first vibrator 4 differs from the frequency of the drive force, the first vibrator 4 undergoes almost no vibration, but the second vibrator 3 which has a resonance point at the frequency of the drive force is resonated by the reaction of the drive force to produce vibration. The vibration generated is perceived by the human body, notifying the user of an incoming call.
With the notifying unit 2, the resonance frequencies of the vibrators 4, 3 inevitably involve variations due to tolerances for the specifications for determining the resonance frequencies of the vibrators 4, 3, such as the configurations, dimensions, materials, etc. of the diaphragms 41, 34, yokes 32, 33 and permanent magnet 31. For example, the thickness of the second diaphragm 34 constituting the second vibrator 3 has a tolerance of 120 μm±8 μm. In the case where the resonance frequency Fv is 100 Hz when the diaphragm thickness t is 120 μm, the variation in the resonance frequency is 100 Hz±10 Hz since the resonance frequency Fv is in proportion to the thickness t raised to the index 1.5.
FIG. 12 shows vibration characteristics a in a solid line as varied by dimensional tolerances, etc. to vibration characteristics b, c in a broken line, respectively. If a vibrator having the vibration characteristics b involving a variation is driven at the resonance frequency of the vibration characteristics a with no variation, no resonance occurs, and the amplitude of the vibrator will greatly decrease from a peak value Wp at the resonance point to a value W′. Thus in the case where the notifying unit is driven with a drive signal of given frequency without considering the variation of the resonance frequency, there arises the problem that variations occur also in the amplitude of the vibrator, failing to produce a satisfactory notifying effect.
Further portable telephones in recent years can be set in various operation modes, for example, to display the telephone number of the caller upon receiving an incoming call or to serve as a pager. In conformity with such a wider variety of operational functions, there arises a need for the notifying unit to give notification not only of incoming calls but also of the various modes in which the telephone is set.
Accordingly, a first object of the present invention is to provide a notifying device which produces to satisfactory notifying effects despite the variation in resonance frequency, and a wireless communications system incorporating the device.
A second object of the invention is to provide a wireless communications system comprising a notifying device adapted for different kinds of notifying operations including notification of incoming calls to give satisfactory notifying effects despite the variation in resonance frequency.